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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2018-408
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2018-408
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Dec 2018

Research article | 10 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

A novel study of the morphology and effective density of externally mixed black carbon aerosols in ambient air using a size-resolved single-particle soot photometer (SP2)

Yunfei Wu1, Yunjie Xia1,2, Rujin Huang3, Zhaoze Deng4, Ping Tian5, Xiangao Xia4, and Renjian Zhang1 Yunfei Wu et al.
  • 1Key Laboratory of Regional Climate-Environment for Temperate East Asia (RCE-TEA), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2University of Chinese Academy of Sciences, Beijing, 100049, China
  • 3Key Laboratory of Aerosol Chemistry and Physics, State Key Laboratory of Loess and Quaternary Geology, Institute of Earth and Environment, Chinese Academy of Sciences, Xi'an 710061, China
  • 4Key Laboratory of Middle Atmosphere and Global Environment Observat ion (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 5Beijing Weather Modification Office, Beijing 100089, China

Abstract. The morphology of externally mixed black carbon (extBC) aerosols, an important factor affecting radiative forcing, was studied by a tandem method coupling a differential mobility diameter (DMA) with a single-particle soot photometer (SP2). Ambient particles were selected by the DMA, and the size-resolved extBC particles were distinguished from those of a thick coating (internally mixed) and quantified by the SP2. Time differences between the DMA size selection and the SP2 measurement were processed previously, as well as the effects of multicharged particles. Based on the mass-mobility relationship, the fractal dimension of the extBC particles was obtained, with a value of 2.36±0.04. This value is comparable with those of diesel exhaust particles, implying a predominant contribution of vehicle emissions to the ambient extBC in urban Beijing. The effective densities (ρeff) of the extBC in the mobility diameter range of 140–750nm were also derived, with values gradually decreasing from 0.34gcm−3 at 140–160nm to 0.12gcm−3 at 700nm. The ρeff values were generally lower than those measured using the DMA-aerosol particle mass analyzer (APM) system. This was most likely due to the lower BC masses determined by the SP2 compared to those from the APM, since the SP2 measured the mass of pure refractory BC instead of the entire BC aggregate consisting of both refractory BC and nonrefractory components measured by the APM.

Yunfei Wu et al.
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Short summary
A novel system composing of a DMA and SP2 was designed to investigate the morphology and effective density of externally-mixed BC (extBC) in ambient atmosphere. Based on 19-day in-situ measurement in urban Beijing using the system, the fractal dimension of extBC was determined as 2.36 indicating the dominant contribution of diesel exhausts. The loosely chain-like structure of extBC was identified with effective density decreasing from 0.34 to 0.12 g cm−3 in the mobility size range of 140–700 nm.
A novel system composing of a DMA and SP2 was designed to investigate the morphology and...
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